Identifying N2O formation and emissions from a full-scale partial nitritation reactor.

Area of Science:

• Environmental Science
• Environmental Engineering
• Wastewater Treatment

Background:

• Nitrous oxide (N2O) is a potent greenhouse gas.
• Partial nitritation (SHARON) reactors are used in wastewater treatment.
• Understanding N2O formation pathways in these reactors is crucial for emission control.

Purpose of the Study:

• To quantify N2O formation and emissions from a full-scale SHARON reactor.
• To identify the sources of N2O production (aerobic vs. anoxic).
• To assess the impact of operational parameters on N2O emissions.

Main Methods:

• Three-week monitoring campaign of reactor off-gas (N2O, O2, CO2, NO).
• Gas stripping profile analysis to differentiate N2O sources.
• Liquid N2O measurements for validation.
• Dedicated experiments varying dissolved oxygen and anoxic periods.

Main Results:

• Overall N2O emission was 3.7% of the incoming ammonium load.
• 70% of N2O emissions originated from anoxic conditions during standard operation.
• Low dissolved oxygen (<1.0 gO2·m⁻³) and extended anoxic periods increased N2O emissions.
• Off-gas N2O monitoring proved effective for tracking gas-liquid mass transfer (kLa).

Conclusions:

• Anoxic conditions are the primary driver of N2O emissions in SHARON reactors.
• Minimizing or eliminating anoxic periods is the most effective strategy to reduce N2O emissions.
• N2O off-gas analysis can serve as a valuable tool for real-time monitoring of reactor performance.